The statements in this section merely provide background information related to the present invention and may not constitute prior art.
Corrosion is the leading cause of material failure costing billions annually in the United States. The largest sector of corrosion prevention is that of protective, organic and metallic coatings applied to ferric components. Small defects and damage of the protective coating acts as initiation sites for subsurface component degradation. Further enunciation of the effects of corrosion is evident by damage caused from erosion, impact, wear, chemical changes, or a combination of the like. Preventive maintenance applied to damaged or locally corroded areas prevents further corrosion and avoids the costs of component or overall structural replacement. The extent of damage to a painted or coated material can be difficult to evaluate due to a number of factors, not limited to, small flaw size, low contrast between feature and nominal coating, inspection resolution, coloring or staining of surface to be inspected, operator error, and the like. In many circumstances, surface damage and degradation are not the only concerns that exist. For example, subsurface coatings assist with galvanic protection by providing additional resistance to corrosion, nuclear radiation and electromagnetic radiation. That said, failure of a subsurface coating, like surface coatings, can result in failure of a component or entire structure/product. Additionally, small subsurface cracks not readily visible using surface inspection techniques can lead to degradation, fatigue, and ultimately structural failure. Therefore, there is a need in the art to provide a coating that can be used to provide a method for inspecting the integrity of surface and subsurface coatings. Visual inspection is one primary method of damage detection. However, visual inspection has a low probability of detecting small flaws and is time consuming. Therefore, there is a need in the art to provide a coating having increased inspection rates due to increased contrast of flawed areas, and thus resulting in a higher level of detection of flaws overall.
Other techniques also exist for nondestructive evaluation or inspection. For example, Liquid Dye Penetrant (LDP) testing is one primary nondestructive evaluation process. This process may include cleaning the surface to be inspected, applying liquid penetrant dye, removing excess penetrant, applying developing solution, and inspecting surface for flaws. The dye for penetrant inspection is typically of a contrasting color, fluorescent material, or a UV interactive material to enhance detection by visual inspection.
Although used as a primary nondestructive evaluation inspection technique, LPD has its limitations. For example, LPD requires costly consumables for detection. The coating/coating system or component has to be exposed to the coating surface in order to be detected and may be difficult to evaluate the surface for flaws as a result of the small flaw size, low contrast between feature and nominal coatings, inspection resolution, coloring or staining of the surface to be inspected, and/or operator error, and the like. Similarly, LPD inspection is limited to a minimum depth and is not practical for large area detection.
Magnetic Particle Inspection (MPI) is an alternative nondestructive evaluation inspection technique for ferric structures. MPI may include applying to the surfaces of inspection UV reactive material, applying a magnetic field to the component of inspection and inspecting the part under UV illumination. MPI is typically only conducted on small components due to the requirement of magnetization of the component to be inspected. Similarly, like LPD, MPI requires additional consumables, is time consuming, and is limited to relatively small magnetically compatible components.
Coatings have been shown to be an effective way of monitoring, determining and detecting corrosion, damage, flaws/defects, and the like, and as such, have been the subject of several patents. For example, U.S. Pat. No. 2,320,842 to Arnold et al discloses the use of luminescent pigment for primers and automotive paint to determine thin top coatings. U.S. Pat. No. 4,327,155 to Hanneman discloses using a luminescent layer of flame spray coatings for detection of penetration depth of erosion for ceramic and metallic components. U.S. Pat. No. 2,976,716 to Haven teaches a method of determining wear patterns using multi-layer paint with color variations. Lastly, U.S. Pat. No. 6,974,641 to Choy et al discloses a thermal barrier coating with a thermal luminescent indicator material embedded therein. Although the above-mentioned references disclose various coatings used to detect wear, erosion, and other desirable evaluation indicators, the above references do not disclose a technique for producing “smart” coatings or coating systems for health monitoring and/or nondestructive evaluation and early detection that when stimulated, apprise of failure zones that include corrosion sites, damage regions, flaws, defects within a protective layer, and the like.
The present invention addresses needs in the art for improved coating and coating systems for in-situ health monitoring, subsurface inspection, nondestructive evaluation and/or early detection of corrosion, damage, failure, flaws, defects, and the like.